Deciphering the mechanisms underlying cancer initiation and progression is of primary importance to human health. More than 1.5 million new cancer diagnoses are estimated to occur in 2014, with a five-year relative survival of 66%. Much effort has gone into describing the nuclear genomic determinants of oncogenesis, focusing on the tumorigenic phenotypes derived through genetic instability and acquired mutations. Far less attention has been directed toward the mitochondria and its genome. Emerging research within the past few years has strengthened links between mitochondrial DNA integrity, cancer metabolism, and tumor progression. The glycolytic shift characteristic of many tumors, called `aerobic glycolysis', may support mtDNA integrity during neoplastic transformation, and could have other pro-tumorigenic effects. This proposal will investigate the hypothesis that the shift in tumor metabolism from oxidative phosphorylation to glycolysis reduces mitochondrial DNA mutation rate, production of genotoxic reactive oxygen species generated through respiration, and cancer cell death susceptibility. To test this hypothesis, alterations to cancer cells' metabolc state will be achieved through genetic engineering to disrupt nutrient processing and strict control of systemic oxidative phosphorylation substrates to enforce metabolic pathway shift. To evaluate effects of reduced oxidative phosphorylation on cancer cell mitochondrial genomes, mutation load will be quantified using a new droplet digital PCR technique for accurate determination of mutation frequency. Reactive oxygen species generation will be monitored with fluorescent indicators to visualize cancer cell oxidative stress from altered metabolic flux. Finally, intrinsic apoptosis pathway activity following pro-apoptotic stimuli will be characterizedin the context of reduced oxidative phosphorylation by evaluating apoptosis-inciting mitochondrial membrane depolarization and activation of early programmed cell death mediators. The proposed research has potential to advance understanding of the determinants of mitochondrial mutagenesis and to identify mechanisms supporting cancer progression, which may reveal new therapeutic targets for clinical intervention.